In a way that shows a lack or shortage; inadequately.
From deficient + -ly (adverb suffix). Deficient itself comes from Latin deficiens, meaning 'failing' or 'lacking.'
This adverb is rarely used today because we prefer saying 'inadequately' or 'insufficiently,' but it's a perfect example of how English drops words that feel too clunky to say out loud!
Complete word intelligence in one call. Free tier — 50 lookups/day.